The road to Damascus had been the Syrian opposition's most difficult journey. Now, after one decisive and deadly strike, the world's oldest capital appears in reach.

As the dust settled at the national security building, a transformation unthinkable only hours earlier was under way. Three of the regime's leaders lay dead around the table where they had been holding a weekly crisis meeting: the deputy defence minister, Assef Shawkat, the defence minister, Dawoud Rajha, and the military committee leader, Hassan Turkmani, all key figures in the Middle East's most ruthlessly efficient police state.

Of the three, Shawkat had long been the main target. His influence and power had been unmatched since the popular uprising began nearly 17 months ago. Shawkat was, as Syrian rebels like to say, the keeper of the secrets.

Every strategic decision about the crackdown carried out by President Bashar al-Assad's regime that had steadily morphed into full-blown war had passed across his desk. He was an essential part of the inner sanctum. In many eyes, he was a symbol of its infallibility.

Within minutes of the assassinations, the regime had acknowledged them – an unusual event in a police state that has been reluctant to admit setbacks throughout the uprising. And an event that sparked fears not all was as it seems. Information warfare has been a feature of the Syrian conflict, where both sides routinely clutch at straws.

The announcement, made first through Hezbollah's television station in Lebanon, then confirmed by the state television in Syria, electrified Damascus, where rebel groups had for three days been battling regime troops that had been considered to be the capital's staunchest defenders.

Some of the units regarded as "diehards" immediately swapped sides, according to activists and residents in Damascus. Others are reported to have abandoned their tanks and fled.

The reaction was the same in all the hotspots of the uprising. A video posted on the internet showed hundreds of men defecting in Homs. Another appeared to show cars streaming out of Aleppo to reinforce the rebels.

In Idlib province, envoys from opposition villages travelled to pro-regime enclaves imploring them to join the revolution. The mood, bleak and full of foreboding only last week as shortages and siege began to take hold, was reported to be euphoric. Shawkat's death in particular seemed to strike a chord among loyalists and rebels alike. "Stability with Assad," was what we were supposed to get, said Thaer Nakhli, speaking by telephone from the Damascus suburb of Down. "He says stick with me – and he can't protect the capital."

On the opposition side, Mohammed Nazhar, a lieutenant in the Free Syrian Army, said a rebel intelligence unit had been working to co-opt key aides from within the regime to use as assassins. The message it wanted to convey was clear: who in the regime was safe if the most feared of them all could be reached so easily?

Removing a power base was always going to lead to a vacuum in Syria, just as it had done in Iraq, Yemen, Egypt and Libya. Swamping the capital with thousands of fighters and opposition supporters had clearly been a tactic in the aftermath of Wednesday's strike. As night fell in Damascus, live web-streams showed scenes of celebrations on the streets of some areas that had been battlegrounds on Tuesday morning.

Men and youths milled about, waving flags and dancing as if they had nothing to fear. And for a while, they might well feel they do not.

The coming days, however, will give a sense of whether the rebel gains, as dramatic as they undoubtedly are, can be sustained, or consolidated. To get from this point to outright control of Damascus, as opposed to the bragging rights they now have in some areas, will need a continued momentum.

Whether the fear factor has been broken will be decisive. Have the opposition's gains galvanised waverers in the regime to join them? Does the regime still have the capacity to shut down violence with overwhelming force? Does it have a new crew of leaders who can command the same loyalty and instil the same fear?

Despite Wednesday's tumultuous events, the key items on the opposition's wish list – defections and weapons re-supplies – have not until this point given them a critical mass. And despite yesterday's setback, reprisals and a counterattack by the regime still do seem inevitable.

Syria's rebels have surprised many this week with their ability to seize and hold ground and take the fight to the regime in its most closely guarded areas.

No longer is the guerrilla force a patchwork of disparate militias. Its attack in Damascus was co-ordinated and resilient. In the capital at least, the fight is now one standing army against another.

Damascus has seen empires rise and fall. Throughout the four decades of the Assad regime, it has been central to some of the Middle East's most defining moments. But in recent years, it has seen few more important days than this.

The opposition is still reeling from what it managed to do . The quest to finish the job is not entirely its own.

Whether the deaths of the strongmen can bring the masses around will determine whether this is indeed the beginning of the end – or the start of something far worse.